Not applicable.
Not applicable.
The present invention relates to dispensing volatile materials such as insecticides, insect repellants, fragrances, and deodorizers. It provides mats designed to be placed on an electric heater to release the volatile material when the mat is heated.
It is known in the art to impregnate or coat a solid porous cellulosic mat with a volatile material, and/or to place a volatile material in a metal pan-like mat structure. These mats are then placed on heaters to cause the volatile to vaporize into the ambient air. See generally U.S. Pat. No. 6,031,967 and WO 99/66791. The disclosure of these publications, and of all other publications referred to herein, are incorporated by reference as if fully set forth herein.
However, there can be a time lag between the initiation of the heating of the mat and when the concentration of active in the room is at a desired level. For example, when the mat contains an insecticide, it may take a few minutes before the desired level of protection from mosquitoes or other insects is achieved. This is a particular problem where the product is designed to provide a very slow, prolonged release of active (e.g. to provide overnight protection against mosquitoes).
To minimize the time lag, one could try increasing the concentration of active on the mat. However, such actives are often costly, and in any event the increased concentration may lead to unnecessarily high levels of insecticide or other active being dispensed into the air after the initial period.
Another approach to try to solve this problem would be to modify heaters so that they work at one heat during an initial phase and then work at a reduced heat at all other times. However, this would require extensive cost in revising existing heaters and, in any event, would unnecessarily increase the cost of heaters in the future.
U.S. Pat. No. 5,657,574 proposed a mosquito coil having a uniform concentration of insect control agent spread throughout it, but with the coil having an enlarged ignition end. When the coil is first lit an extra burst of insecticide is dispensed because more of the coil is burnt at that time. However, this approach is not suitable for a mat where the entire mat is to be placed on the heater at once.
WO 99/66791 provided a slab-type mat system for insertion in an indexed fashion into a heater. Discrete regions of the mat are heated in sequence. The primary purpose of the slab is to provide a mechanism for indexing a new mat section over the heater when the preceding section had been used up. However, the publication also describes that the sequential regions could carry different volatile ingredients or different concentrations of the same volatile ingredient. One example that is given is providing a high concentration section to be used at night and a low concentration section to be used during the day. Unfortunately, this requires the user to sequentially move the slab when the next stage of usage is desired.
Complicating matters is the fact that most of the inexpensive heaters used for this purpose take some time to warm up, and many do not have a fully uniform heat presentation across their face. For example, many have a hot region in the center, with progressive cooling outward. In the past, this has caused some insecticides to degrade due to exposure to the too hot central section.
Accordingly, a need still exists for an improved volatile dispensing mat.
The present invention provides a mat for dispensing volatile vapors when heated. In one form there is a first mat substrate region having a first volatile material with an active selected from the group consisting of insect control agent, fragrance, deodorizer, and any combination thereof. There is also a second mat substrate region having a second volatile material with an active selected from the group consisting of insect control agent, fragrance, deodorizer, and any combination thereof. The first volatile material of the first mat substrate region releases at an effective rate greater than does the second volatile material of the second mat substrate region, either because of the higher and lower volatility characteristics of the first volatile material versus the second volatile material or because of selected differences between the first and second mat substrate regions. Preferably, the first region is a central region, the second region is an outward region around the central region, and the first volatile material is different from the second volatile material. A volatile material is defined as releasing at a greater or lesser xe2x80x9ceffectivexe2x80x9d rate as the intended effect of the active constituting or contained in the volatile material is achieved at a faster or slower rate.
The term xe2x80x9cmatxe2x80x9d is used herein to include any generally flat, thin, extended structure suitable for use with conventional mosquito mat holders, regardless of material, precise outline, texture, and other physical features such as through-holes, incorporated metallic pans, and the like. The typical commercial mosquito mat is usually a generally rectangular card made of a fibrous material, although, as just stated, the term xe2x80x9cmatxe2x80x9d is not confined to that particular shape or material. The term xe2x80x9cinsect controlxe2x80x9d is defined to mean killing, repelling, or otherwise altering the behavior or development of insects. xe2x80x9cInsect control agentxe2x80x9d is used herein in its broadest sense to include not only insecticides and repellants but also growth regulators and other agents capable of achieving insect control. xe2x80x9cInsectxe2x80x9d is defined to mean actual insects as well as spiders, millipedes, and other small animals commonly controlled in the same manner or with the same agents as are insects.
The first and preferably central region can be made of a metallic or other substrate which transmits heat faster than a surrounding substrate, preferably made of cellulose. This will cause different vaporization rates, even where the volatiles are the same.
One can alternatively (or in addition) retard or increase the rate of release by the selection of suitable solvents, binders, actives, and active concentrations. We prefer to use a highly volatile active for the first region, such as transfluthrin or prallethrin, esbiothrin, d-allethrin, S-bioallethrin and dichlorvos, as well as to select a metallic, thin, and nonporous substrate for the first region which will release the volatile very quickly. Particularly preferred is where the active in the volatile material of the second region is transfluthrin and the active in the volatile material of the first region is d-allethrin.
In especially preferred forms, the first and second regions are comprised of materials differing with respect to a material property selected from the group consisting of thickness, thermal conductivity, porosity, and combinations thereof. In such a case, the second region would preferably be in the form of a slab having a bore therethrough, and the first region would preferably be defined by a metal foil cup positioned in the bore. Preferably the bore and cup would be centrally located in the slab, xe2x80x9ccentrallyxe2x80x9d located being construed to mean generally centrally located or at least so located that slab material completely surrounds the bore.
Alternatively, the second region can be a ceramic slab having a recess in an upper side, and the first region can be defined by a ceramic glaze lining the recess.
In yet another variant, the second region can be a frame of cellulosic material and the first region can be a metallic tray having a recessed center extending preferably at least to the bottom surface of the frame or even further, whereupon it actually supports the frame.
In yet another form, the invention provides a mat for dispensing volatile vapors when heated. Again, there are first and second mat substrate regions, each having a volatile material with an active selected from the group consisting of insect control agent, fragrance, deodorizer, and a combination thereof. Regardless of their juxtaposition relative to each other (e.g. side by side; central and surrounding donut), the first and second regions are comprised of materials differing with respect to a material property selected from the group consisting of thickness, thermal conductivity, porosity, and combinations thereof.
In still another form, the invention provides a method for dispensing volatile vapors. One positions a mat on an electric heater. The mat has a first and a second mat substrate region having first and second volatile materials, respectively, the volatile materials each including an active selected from the group consisting of insect control agent, fragrance, deodorizer, and combinations thereof. One then simultaneously heats both the first and second mat substrate regions such that the active in the first volatile material is vaporized from the first region at a greater effective rate than the active in the second volatile material from the second region.
When used as an insect control device, the device of the invention allows the user to achieve desired protection very quickly, without sacrificing long-term protection. When dispensing a deodorizer or fragrance, the invention has the advantage of covering over existing malodors very quickly (e.g. in a bathroom), without sacrificing the ability to provide fragrance over the long term.
Importantly and surprisingly, the present invention is capable of turning a disadvantage of inexpensive heaters (non-uniform heating across the heating face) into an advantage. This is achieved by centrally placing the fast release section.
These and still other advantages of the invention will appear from the following description. In the description reference is made to the accompanying drawings in which there is shown by way of illustration preferred embodiments of the invention. However, the claims should be looked to in order to judge the full scope of the invention.